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71.
Krystyna Szeroczyńska Andrzej Tatur Jan Weckström Michał Gąsiorowski Agnieszka M. Noryśkiewicz Elwira Sienkiewicz 《Journal of Paleolimnology》2007,38(1):25-47
A 2.5-m-long sediment core was retrieved from Lake Somaslampi, a small lake located in a kame field on the north slope of
the Scandes Mountains in Finnish Lapland. Holocene environmental changes were inferred from the lithological, geochemical,
pollen, diatom and Cladocera records stored in the lake sediment. The chronology was based on six radiocarbon AMS dates supported
by a palynological control chronology. The sediment profile consists of a glacial sedimentary sequence truncated by a lacustrine
one. A hiatus, tentatively correlated with climate cooling and advances of glaciers during the 8.2 ka yrs BP “Finse cooling
Event”, occurs between these sequences. The glacial sequence was composed of fluvioglacial clastics, smoothly changing into
glacio-lacustrine diatomaceous ooze deposited in a meromictic proglacial lake that covered the kame field. The meromixis was
probably caused by the greater depth of the lake, the extended ice-cover, and the microbial mats covering large areas of the
lake bottom. A distinct change in the biota of the glacio-lacustrine sediments indicates higher trophic conditions than during
deposition of the fluvioglacial clastics. The late-Pleistocene vegetation was characterised by subarctic birch tundra vegetation
(Betula–Salix–Ericaceae) with low biodiversity gradually changing to Betula–Pinus dominance in the early Holocene. The lake was deep and had a diatom inferred pH ~ 7 indicated also by the dominance of planktonic
Cladocera.
The base of the lacustrine sediment sequence (6,650–6,300 cal. BP) consisted of loess-rich sediment indicating an increase
in eolian activity. This is also supported by the pollen record, which is dominated by more long-distant taxa such as Alnus and Pinus, and by the increased C/N ratio of the sediment. After the initial meromictic phase of the lake, an abrupt lowering of the
water level occurred. Lake Somaslampi was isolated from the larger Pre-Lake Somas basin and became holomictic, shallow, much
warmer and more productive, until the deterioration of climate around 3,000 yr BP and the increased input of clastics from
the tundra soils. The vegetation followed the general climatic trend by gradually changing from the dominance of Betula and Pinus to the dominance of more tundra-related vegetation like Poaceae and Cyperaceae. However, the higher frequencies of planktonic
Cladocera and centric diatoms in the most recent sediments indicates higher trophic conditions, increased turbulence and a
prolonged ice-free period, which can possibly be linked to the recent climate warming especially in areas of higher altitude
and latitude. 相似文献
72.
Wolfgang Dörr Andrzej Żelaźniewicz Paweł Bylina Janina Schastok Wolfgang Franke Udo Haack Cyprian Kulicki 《International Journal of Earth Sciences》2006,95(2):341-349
The Odra Fault Zone of southwestern Poland is a NW-trending horst marked by gravimetric and magnetic anomalies and composed of high- to low-grade metamorphic and igneous rocks which are only known from boreholes. This zone embraces a concealed border between Variscan internides and externides. It also contains an array of several I-type, metaluminous to peraluminous, high potassic granitoid bodies which intruded earlier metamorphosed rocks. Except for one case, they remain unfoliated and undeformed, and presumably play a role of stitching plutons at the suture between two obliquely colliding terranes. U–Pb TIMS dating of single zircons from one foliated and one unfoliated granitoid samples yielded identical concordant ages of 344±1 Ma (Tournaisian). They resemble a Pb–Pb age of 350±5 Ma obtained for S-type granitoids from the Luckau area further west in Germany, which is generally regarded as an eastern segment of the Mid-German Crystalline High. Carboniferous granitic intrusions in the high are generally younger (340–290 Ma). Correlations of the the Odra Fault Zone with the Mid-German Crystalline High appear plausible, but by no means certain and require further confirmation. 相似文献
73.
The presence of natural gas in the pore space of reservoir rocks results in a significant decrease in P-wave velocity. Even low gas saturation can generate seismic anomalies (DHI) and false image of gas accumulation of economic importance. This article presents an attempt to evaluate gas saturation from 2D seismic section in the Miocene sandstone strata in the south-eastern part of the Carpathian Foredeep. The ESTYMACJA program and the Biot-Gassmann model were used to study the dependence between elastic parameters and saturating fluids (water and gas) recorded in wells. Series of calculations was carried out using a method of fluid substitution for various gas saturation. The applicability of seismic data for evaluating gas saturation of reservoir beds was assessed with the use of 1D modelling (synthetic seismograms) and 2D modelling (theoretical seismic section) calculated for different gas saturation. The proposed methodology can be used to identify low and high gas-saturated zones and contour the reservoir. 相似文献
74.
Methods of computing the deflections of flexible vegetation elements under the dynamic pressure of water were presented in the paper. Two methods, based on Euler-Bernoulli beam theory, were discussed, one designed for small deflections and the other, generalized one, also for larger deflections. The choice of the method for computations of deflections was discussed from the perspective of the computation of flow velocities above flexible vegetation. Computational results were compared with laboratory experiments and it was found that the simplified, computationally less expensive method may be used in many practical situations without deterioration of the results. 相似文献
75.
The paper summarizes the findings about a seismic event on January 22, 2010, near Bełchatów, Poland, in terms of data, event
location, magnitude and source parameters. 相似文献
76.
We inferred the temperature and environmental conditions of Smreczynski Staw Lake in the Tatra Mountains, southern Poland,
from a sediment record covering the last 1,500 years. Paleobiological methods (cladocera, chironomid, and diatom analyses)
were used together with sedimentological analysis and dating. These studies provide new information about the timing and character
of climate fluctuations during the Little Ice Age (LIA). The Medieval Warm Period ended in the Tatra region at the beginning
of the thirteenth century, followed by the first episode of the LIA. The LIA was a relatively long but unstable period. The
first part of the LIA was cold in the Tatra Mountains, without evidence of increasing precipitation, while the second part,
after AD 1540, was cold and humid. The LIA terminated in the Tatra Mountains at the beginning of the twentieth century, although
some aspects of its climatic and sedimentological regime continued until the 1920s. We also found some evidence of warming
and acidification during the twentieth century. 相似文献
77.
Edyta Puskarczyk Paulina Krakowska Mariusz Jędrychowski Magdalena Habrat Paweł Madejski 《Acta Geophysica》2018,66(6):1453-1461
The main goal was the analysis of parameters describing the structure of the pore space of carbonate rocks, based on tomographic images. The results of CT images interpretation, made for 17 samples of Paleozoic carbonate rocks were shown. The qualitative and quantitative analysis of a pore system was performed. Objects were clustered according to the pore size. Within the clusters, the geometry parameters were analysed. The following dependences were obtained for carbonate rocks, also for individual clusters (due to the volume): (1) a linear relationship (on a bilogarithmic scale) between the specific surface and the Feret diameter and (2) a strong linear relationship between specific surface area and Feret diameter and average diameter of the objects calculated for the sphere. The results were then combined with available results from standard laboratory tests, including NMR and MICP. 相似文献
78.
Rafał Kroczak Joanna Fidelus-Orzechowska Anna Bucała-Hrabia Tomasz Bryndal 《山地科学学报》2018,15(12):2561-2578
Land use and land cover (LULC) changes and their impact on the mountain environment were studied in six catchments (~10 km2 each) in the Polish Western Carpathians from the mid-19th century to the early 21st century. The analysis of cadastral and orthophoto maps indicates that during the investigated period, the forest area increased, quantified by an annual change index (Annch), between +0.12% to +0.27%, with a decrease of arable land index to–0.45% and–2.28% in the analysed catchments. LULC changes were accompanied by a continuous increase in settlement developments (residential and farming houses) by 50%-140% as well as significant changes related to their spatial distribution. Abandonment of arable land and forest succession have resulted in the geomorphological transformation of hillslopes, which predominantly includes a decrease in used road density, their transformation to road cuts and gorges. Overpopulation and the domination agriculture in the past caused the expansion of unpaved roads density and then the fragmentation of hillslopes, as well as the development of agricultural terraces. 相似文献
79.
Pawe? Wajer 《Icarus》2010,209(2):488-493
We study the dynamical evolution of Asteroids (164207) 2004 GU9 and 2006 FV35, which are currently Earth quasi-satellites (QS). Our analysis is based on numerical computation of their orbits, and we also applied the theory of co-orbital motion developed in Wajer (Wajer, P. [2009]. Icarus 200, 147-153) to describe and analyze the objects’ dynamics. 2004 GU9 stays as an Earth QS for about a 1000 years. In the present epoch it is in the middle of its stay in this regime. After leaving the QS orbit near 2600 this asteroid will move inside the Earth’s co-orbital region on a regular horseshoe (HS) orbit for a few 1000 years. Later, either HS-QS or HS-P transitions are possible, where P means “passing”. Although 2004 GU9 moves primarily under the influence of the Sun and Earth, Venus plays a significant role in destabilizing the object’s orbit. Our analysis showed that the guiding center of 2006 FV35 moves deep inside the averaged potential well, and since the asteroid’s argument of perihelion precesses at a rate of approximately , it prevents the QS state begin left for a long period of time; consequently the asteroid has occupied this state for about 104 years and will stay in this orbit for about 800 more years. Near 2800 the asteroid’s close approach with Venus will cause it to exit the QS state, but probably it will still be moving inside the Earth’s co-orbital region and will experience transitions between HS, TP (tadpole) and P types of motion. 相似文献
80.
Refined timing and kinematics for Baltica–Avalonia convergence based on the sedimentary record of a foreland basin 
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下载免费PDF全文 Stanisław Mazur Szczepan J. Porębski Artur Kędzior Mariusz Paszkowski Teresa Podhalańska Paweł Poprawa 《地学学报》2018,30(1):8-16
The Caledonian foreland basin of Poland onlaps the SW slope of the East European Craton and is elongated in a NW–SW direction along the margin of the Baltica palaeocontinent. The base of the synorogenic clastic wedge rises in age from Llandovery to Ludlow between NW and SE Poland, respectively. As the initial influx of orogen‐derived detritus can be unequivocally identified, this diachronism documents a southeastward migration of the basin depocentre, parallel to the present‐day Caledonian Deformation Front. Our best‐fit plate model shows an oblique collision of Baltica and Avalonia, the latter initially indenting the Baltica margin in the NW. Afterwards, Baltica was progressively underthrust beneath Avalonia towards the SE in response to the oblique soft‐mode closure of the Tornquist Ocean. The final deformation event within the Caledonian foreland took place in the earliest Devonian as a far‐field effect of sinistral orogen‐parallel displacements along the Iapetus suture. 相似文献